The German patent specification 26 49 042 discloses an implant for the human vertebral column including pedicle screws to be threaded into a verebra body and having an open-ended slot in the screw for the acccommodation of a compression rod. The compression rod is fixed to the screw head by nuts on the compression rod on both sides of the screw head. A pressure distribution plate is located below the screw head and is matched to the shape of the vertebra body. Frequently, the known implant is used pairwisely on both sides of the vertebra body, with the compression rod being adapted to the curvature of the vertebral column by bending it correspondingly. The stability of the compression rod is relatively low. A mutual bracing of the pairwisely located implants is not provided.
The German patent specification 32 19 575 discloses a correction implant for human vertebral columns using bone screws. The bone screws are connected with corner pieces interconnected in turn by a tension lock. By means of the tension lock, the distance between the bone screws can be varied. It is also known to tighten pairwisely arranged implants by tension wires. It is known that wires can be only loaded with tension and not with thrust or torsional forces. It is further disadvantageous with the known implant that the screws have to be actuated from different directions of access.
From the German patent specification 38 23 737, a correction and retaining means for the vertebral column is known, wherein pedicle screws are linked to support parts interconnected by a first and a second pair of threaded rods. The first pair of threaded rods interconnects the pedicle screws on one side of the vertebral column while the threaded rods of the second pair are crossing. The structure of the known correction implant is relatively expensive. The actuation of the screws takes place from different directions which means an additional difficulty for the surgeon.